Serial Number Mask - Manually Added SN

A user added a Serial Number manually. They did not add a mask information. I tried to DMT the Mask in but, it won’t allow me to change it and the Form it’s disabled. I’m guessing because there are transactions against it(which were just status changes). We need that information in there for another system. Anybody know of a way to update it?

Any help would be awesome!

Thanks!
Caleb